For reasons including improved efficacy of action and reduced frequency of administration, there is considerable interest in the development of pharmaceutical and veterinary formulations capable of controllably releasing active agents for sustained periods (e.g. up to 6 months or more). Types of pharmaceutical agents that would particularly benefit from the development of such formulations are those which are typically administered by patients themselves over long periods (e.g. insulin for diabetes treatment, and gonadotropin-releasing hormone (GnRH) agonists for reproductive control and treatment of sex hormone-dependent diseases and conditions) and require high levels of patient compliance. In the veterinary context, sustained release formulations would reduce the stress often caused to the animal and veterinarian/owner alike by the need for repeated administration of active agents.
The present applicant's have found that sustained release of at least one active agent in humans and other animals for periods of 7 days up to about 2 years, can be achieved by using a solid formulation comprising stearin as an excipient in combination with a substance which, while not wishing to be bound by theory, appears to form pores and/or cracks in the excipient to enable the release of the active agent(s).